This project proposes to synthesize a number of ATP analogs. They will be tested as potential substrates, reversible and/or irreversible inhibitors of myosin and actomyosin systems. The synthesis of both purine and phosphate modified analogs is contemplated. Particular emphasis will be placed on developing purine modified analogs which potentially will act as site-specific reagents to bind covalently at the active site of myosin. The goal of this project is to characterize the active sites of skeletal, cardiac and smooth muscle myosins as to their subunit location, their amino acid composition and their relationship to the actin binding site. Where appropriate these analogs will also be tested on other more primitive contractile ATPases, such as slime mold myosin or sea urchin sperm tail dynein.